Heavy vehicles, such as trucks, typically include brake systems that pneumatically apply rear service brakes. Additionally, an emergency brake arrangement is included within the brake systems to protect against brake failure in an event of loss of air pressure. The emergency brake arrangement comprises a spring that applies a mechanical brake force if an air pressure loss event occurs.
This type of arrangement utilizes brake actuators that have a service air chamber and a spring chamber. The service air chamber is selectively pressurized to apply a braking force in response to a service brake request. The spring chamber houses a spring that is biased to apply a braking force. Air pressure within the spring chamber acts against the bias of the spring to hold off any braking force that would be imposed by the spring. In an emergency situation such as a loss of air pressure, the bias of the spring automatically applies the service brakes.
This spring arrangement can also be utilized as a parking brake. When a parking brake request is initiated, air is exhausted from the spring chamber and the bias of the spring applies the service brakes to provide a parking brake function. Current braking systems for heavy vehicles utilize a rear axle service brake relay valve and a separate spring brake quick release valve. The rear axle service brake relay valve controls a supply of reservoir air to rear axle service brakes. The spring brake quick release valve provides air to apply or release the parking brake as needed.
Simultaneous application of the service brake and the parking brake, often referred to as compounding, can cause damage to various brake components. To prevent compounding, the rear axle service brake relay valve and the spring brake quick release valve are connected with an air line that delivers service brake air to the parking brake whenever the service brake is applied. If the parking brake is released and a service brake application is made, then service air sent to the spring brake quick release valve has no effect because the service air is blocked by a two-way check valve included within the spring brake quick release valve. If the parking brake is applied then there is no pressure to block the service air from opening the two-way check valve. Service air can then enter the spring brake quick release valve, which then delivers air to the spring brake chambers, which reduces the applied force of the spring. This is often referred to as anti-compounding.
This traditional configuration has some disadvantages. The spring brake quick release valve and the rear axle service brake relay valve each require a certain amount of mounting space within the vehicle, as well as requiring separate mounting hardware. This increases cost and assembly time. Also, the air line that extends between the rear axle service brake valve and the spring brake quick release valve to prevent compounding takes up valuable mounting space within the vehicle and increases cost. Further, the air line is vulnerable to damage, which could result in a loss of air pressure, and consequently reduced braking performance.
It is desirable to reduce the cost of the brake system while still providing service, emergency, and parking functions in an efficient and controlled manner. Moreover, it is desirable to reduce the complexity of the brake system and to reduce installation and assembly times. Finally, there is also a need to reduce the overall number of components within the system to reduce potential damage areas, as well as overcoming other deficiencies identified within the prior art system discussed above.